This proposal outlines an experimental program for investigating the structure of the glycoprotein hormones (gonadotropins, follicle and thyroid stimulating hormones). These homones are unique among polypeptide hormones in that they possess two nonidentical, noncovalently-linked subunits whose functional significance is poorly understood. The proposed research will emphasize the use of intrinsic and extrinsic fluorescence probes to elucidate the kinetic mechanism of the dissociation and recombination of the subunits as well as the structural changes which accompany those reactions. Where possible, the fluorescent probe, 1,8-anilinonaphthalene sulfonate (ANS) will be used to measure the rates of these reactions. The ligand-induced self-association of these hormones in the presence of ANS will be characterized and efforts made to determine the biological significance of that interaction. Differential absorption spectroscopy will be used to evaluate the solvent-exposure of aromatic residues in the intact hormones and isolated subunits. The effects of chemical modification of the subunits on the kinetic and structural aspects of their interaction with unmodifid subunits will be evaluated. The extensive homology between the corresponding subunits of different hormones will be used as a tool to identify those regions of primary structure which are involved in the subunit interactions and other functions.